Diluted solution production method and diluted solution production apparatus

ABSTRACT

A diluted solution production method of the present invention is a diluted solution production method of producing a diluted solution of a second liquid by adding the second liquid a first liquid, the method including feeding the first liquid to a first pipe; and controlling pressure in a tank that stores the second liquid to add, through the second pipe that connects the tank to the first pipe, the second liquid to the first liquid in the first pipe. Adding the second liquid includes measuring a flow rate of the first liquid or the diluted solution that flows through the first pipe; measuring a component concentration of the diluted solution; and controlling the pressure in the tank, based on the measured values of the flow rate and the component concentration, so as to adjust the component concentration of the diluted solution to a specified value.

This is a divisional application of U.S. patent application Ser. No.15/509,047, filed Mar. 6, 2017, which is a National Stage entry ofInternational Application No. PCT/JP2015/072108, fled on Aug. 4, 2015,which claims the benefit of Japanese Patent Application No. 2014-187804,filed on Sep. 16, 2014. The entire disclosure of each of theabove-identified applications, including the specification, drawings,and claims, is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a diluted solution production method ofproducing a diluted solution and a diluted solution production apparatustherefor.

BACKGROUND ART

In a process for manufacturing semiconductor devices or liquid crystaldisplays, a diluted solution obtained by diluting a chemical liquid,such as aqueous ammonia, with ultrapure water is used as a cleaningliquid for cleaning silicon wafers or glass substrates for liquidcrystal panels. As a method of producing the diluted solution, there isknown a method of adding a minute amount of a chemical liquid toultrapure water supplied to a point of use, and various proposals havebeen made therefor.

For example, Patent Literature 1 proposes a method of adding a chemicalliquid in a chemical tank to a pipe that carries ultrapure water byusing a chemical liquid supply pump. In this method, electricconductivity of ultrapure water to which the chemical liquid has beenadded (diluted solution of chemical liquid) is measured, and based onthe measured value, the amount of the chemical liquid to be added isadjusted.

Patent Literature 2 proposes a method of adding a chemical liquid byusing a plurality of small pipes equipped with valves and connected inparallel between a circulation pipe that circulates ultrapure water anda feeder of the chemical liquid. In this method, the pressure at thetime of adding the chemical liquid to the circulation pipe is adjustedto a certain fixed value, and the amount of the chemical liquid suppliedto the circulation pipe is controlled in accordance with the number ofthe valves that are opened.

Furthermore, Patent Literature 3 proposes a method of adding a chemicalliquid by using a chemical supply pipe that connects a cleaning liquidsupply pipe to a chemical liquid storage container. In this method, theamount of the chemical liquid added from the chemical supply pipe to thecleaning liquid supply pipe is controlled by adjusting the pressure ofgas supplied to the chemical liquid storage container based only on theflow rate of the cleaning liquid in the cleaning liquid supply pipe.

CITATION LIST Patent Literature

Patent Literature 1: JP2000-208471 A

Patent Literature 2: JP2003-311140 A

Patent Literature 3: JP3343776 B

SUMMARY OF THE INVENTION Technical Problem

However, the above methods of producing a diluted solution disclosed inPatent Literatures 1, 2, and 3 have the following problems,respectively.

In the method of producing a diluted solution disclosed in PatentLiterature 1, when the chemical liquid in the diluted solution hasuneven concentration due to the pulsation of the chemical liquid supplypump, or when a high dilution ratio is set, it is necessary to store thechemical liquid, which is preliminarily diluted to some extent, in atank before adding the diluted chemical liquid to ultrapure water.

In the method of producing a diluted solution disclosed in PatentLiterature 2, it is necessary to install a plurality of small pipesequipped with valves, which complicates the apparatus structure.Furthermore; since the concentration of a producible diluted solution isdetermined by the number of installed small pipes, it is difficult toaccurately produce the diluted solution that will have a specifiedconcentration.

In the method of producing a diluted solution disclosed in PatentLiterature 3, the pressure in the chemical liquid storage container isadjusted based only on the flow rate of the cleaning liquid. Accordinglywhen the chemical concentration in the chemical liquid storage containerfluctuates due to vaporization, degradation, or the like, theconcentration of the diluted solution to be obtained deviates from thetarget value.

Accordingly, the present invention has been made in view of the abovedescribed problems, and it is therefore an object of the presentinvention to provide a method of producing a diluted solution and anapparatus for producing the diluted solution with a simple apparatusstructure, the method and apparatus allowing precise addition of aminute amount of a high concentration liquid to a diluent medium so asto provide the diluted solution that will have a specifiedconcentration.

Solution to Problem

According to one aspect of the present invention, there is provided adiluted solution production method of producing a diluted solution of asecond liquid by adding the second liquid to a first liquid, the methodincluding the steps of: feeding first liquid to a first pipe; andcontrolling pressure in a tank that stores the second liquid so as toadd, through a second pipe that connects the tank to the first pipe, thesecond liquid to the first liquid flowing through the first pipe, thestep of adding the second liquid including the steps of: measuring aflow rate of the first liquid or the diluted solution that flows throughthe first pipe; measuring a component concentration of the dilutedsolution; and controlling the pressure in the tank, based on measuredvalues of the flow rate and the component concentration, so as to adjustthe component concentration of the diluted solution to a specifiedvalue.

According to another aspect of the present invention, there is provideda diluted solution production apparatus for producing a diluted solutionof a second liquid by adding the second liquid to a first liquid, theapparatus including: a first pipe that supplies the first liquid; a tankthat stores the second liquid; a second pipe that supplies the secondliquid from the tank to the first pipe; a flowmeter that measures a flowrate of the first liquid or the diluted solution that flows through thefirst pipe; a meter that measures a component concentration of thediluted solution; and a controller that controls pressure in the tank,based on measured values of the flowmeter and the meter, so as to adjustthe component concentration of the diluted solution to a specifiedvalue.

The invention relating to the above-described method and apparatusprovides solutions to the problems relating to the methods of producinga diluted solution disclosed in each of Patent Literatures 1 to 3. Morespecifically, in the diluted solution production method and the dilutedsolution production apparatus of the present invention, the pressure inthe tank that stores the second liquid is controlled so as to adjust apressure gradient generated between the first pipe and the tank that isconnected to the first pipe through the second pipe. As a result, thesecond liquid in the lank is added to the first liquid flowing throughthe first pipe. The second liquid is a chemical liquid to be diluted.The first liquid is a diluent medium, such as pure water. A liquidobtained by adding the chemical liquid to the diluent medium is adiluted solution of the chemical liquid. Such a method of adding thechemical liquid is different from the methods of producing a dilutedsolution disclosed in Patent Literatures 2 and 3 in the followingpoints.

In the diluted solution production method and the diluted solutionproduction apparatus of the present invention, the flow rate and thecomponent concentration of the diluted solution that flows through thefirst pipe are measured. Based on these measured values, an in-tankpressure is adjusted so as to control the amount of the chemical liquidto be added from the tank. On the other hand, in the method of producinga diluted solution disclosed in each of Patent Literatures 2 and 3, theflow rate or the component concentration of the diluted solution thatflows through the first pipe is measured, and based on the measuredvalue, the amount of the chemical liquid to be added from the tank iscontrolled. The term “component concentration” as used herein refers tothe concentration of a component that is derived from the chemicalliquid. The component concentration in the diluted solution can directlybe measured or can be indirectly measured by using an electricconductivity or other parameters.

In the case where the amount of the chemical liquid to be added from thetank is controlled based only on the measured value of the flow rate ofthe diluted solution, when, for example, the chemical concentration inthe tank fluctuates due to vaporization, degradation, or the like, theobtained component concentration of the diluted solution may deviatefrom the target value. In the case where the amount of the chemicalliquid to be added from the tank is controlled based only on themeasured value of the component concentration of the diluted solution,when, for example, fluctuation in the flow rate of the diluted solutionoccurs, the component concentration of the diluted solution in an earlystage of fluctuation in the flow rate may not be maintained at aspecified value. This is because it takes a certain period of time forthe meter to detect the component concentration. Therefore, in order toprovide the diluted solution with a specified component concentrationeven when the flow rate of the diluted solution or the first liquid(diluent medium) fluctuates or even when the concentration of the secondliquid (chemical liquid) in the tank fluctuates, it is necessary tocontrol the pressure in the tank based on both the measured values ofthe flow rate and the component concentration of the diluted solution.

In the present invention, the flow rate and the component concentrationof the diluted solution or the first liquid flowing through the firstpipe are measured, and based on those measured values, the pressure inthe tank is controlled so as to adjust the component concentration ofthe diluted solution to a specified value. Accordingly, as compared withthe methods of producing a diluted solution disclosed in PatentLiteratures 2 and 3, a diluted solution that has an accurate componentconcentration as specified can be obtained.

As described above, the diluted solution production apparatus of thepresent invention controls the pressure in the tank to adjust thepressure gradient between the tank and the first pipe, so that thesupplied amount of the second liquid (chemical liquid) that passesthrough the second pipe is controlled. This flow control is achieved byapplying the Hagen-Poiseuille law concerning head loss in the laminarflow in a circular pipe.

<Hagen-Poiseuille Law>

The flow rate Q [m³/s] of a viscose liquid flowing through a circularpipe having a diameter D [m] and a length L [m] within a fixed period oftime is obtained in the following equation:Q=π×D ⁴ ×ΔP/(128×μ×L).That is, “the flow rate Q [m³/s] is proportional to the 4th power of thediameter D [m], proportional to a pressure gradient ΔP [Pa] between bothends of the pipe, inversely proportional to the length L [m] of thepipe, and inversely proportional to a coefficient of viscosity μ[Pa·s]”. This is called the Hagen-Poiseuille law.

More specifically, the diluted solution production apparatus of thepresent invention can control the supplied amount of the second liquid(chemical liquid) that passes through the second pipe by determining thetype of the second liquid fed to the second pipe and then controllingonly the in-tank pressure. Furthermore, when the diluted solutionproduction apparatus of the present invention is manufactured andactually used, the length L and the inner diameter D of the second pipe,and the viscosity μ of the second liquid fed to the second pipe takefixed values. Accordingly, the flow rate Q in the second pipe canproportionally be controlled by only using the in-tank pressure thatcorresponds to the pressure gradient ΔP between both ends of the secondpipe.

The Hagen-Poiseuille law is based on the assumption that the flow in apipe is a laminar flow. The laminar flow means a regular and orderlyflow. The turbulent flow means an irregular flow.

A rough distinction between the laminar flow and the turbulent flow isgenerally determined based on Reynolds number Re. The laminar flow isconsidered to be in the range of Re≤2300. The turbulent flow isconsidered to be in the range of Re>2300. The Reynolds number Re is anon-dimensional number defined by the ratio between inertia force andviscous force that act on a fluid.

Here, Reynolds number Re [⋅] is defined by:Re=u×D/νwhere ν [m²/s] represents the coefficient of kinematic viscosity, u[m/s] represents the mean velocity in a pipe, and D [m] represents theinner diameter of the pipe. According to the expression, the Reynoldsnumber Re becomes larger with increasing the mean velocity in the pipe u[m/s], with increasing the inner diameter D [m] of the pipe, and withdecreasing the coefficient of kinematic viscosity ν [m²/s]. In thatcase, the flow in the pipe is more likely to be turbulent.

When the flow in the pipe becomes turbulent, the aforementionedHagen-Poiseuille law no longer holds. This makes it difficult to performproportional control of the flow rate Q of the second liquid flowingthrough the second pipe based on the pressure gradient ΔP (which mayalso be referred to as differential pressure below) between both ends ofthe second pipe. Therefore, the assumption that the liquid that flowsthrough the pipe is a laminar flow is important for controlling the flowrate of the said liquid. This is particularly important for carrying outprecise control to adjust the component concentration of the dilutedsolution to a specified value even when the flow rate of the dilutedsolution fluctuates. Therefore, in implementation of the presentinvention, it is preferable that the liquid that flows through thesecond pipe be laminar.

In the present invention, in order to perform more precise control ofthe component concentration of the diluted solution to be produced, thesecond pipe that supplies the second liquid (chemical liquid to bediluted) preferably has an inner diameter of more than 0.1 mm and 4 mmor less.

The reason thereof will be described below. The mean velocity u [m/s] inthe pipe can be defined by the expression u=4×Q/(π×D²) where Q [m³/s] isthe flow rate and D [m] is the diameter. Therefore, the aforementionedexpression of the Reynolds number Re [⋅] can also be expressed byanother expression Re=4×Q/(π×D×ν), where Q [m³/s] is the flow late, D[m] is the diameter, and ν [m²/s] is the coefficient of kinematicviscosity.

Here, in order to make the second liquid that flows through the secondpipe flow at a certain flow rate Q in a laminar flow state, only theinner diameter D of the second pipe can be set accordingly since thecoefficient of kinematic viscosity ν is determined by the flowing liquidand the pipe friction. In this case, as is clear from the above-statedanother expression, if the flow rate is unchanged, the flow in the pipeis more likely to be laminar when the inner diameter D of the secondpipe becomes larger. However, if the inner diameter D) of the secondpipe is made larger, the pressure gradient ΔP between both ends of thesecond pipe becomes smaller as indicated by the Hagen-Poiseuille law.When the pressure gradient ΔP is too small, flow adjustment in thesecond pipe becomes easily influenced by a slight setting error of thein-tank pressure or by the fluctuation in the pressure in the pipe. Thismay lead to a situation where it is substantially impossible to adjustthe flow rate in the second pipe to a specified value.

As is clear from the above description, in the diluted solutionproduction apparatus of the present invention, when the inner diameterof the second pipe is set in a fixed range, the second liquid that flowsthrough the second pipe is likely to in a laminar flow state, and it iseasy to proportionally control the flow rate of the second liquid.

In examples as shown in Table 1, when the inner diameter D of the secondpipe is more than 4 mm, the flow is more likely to be turbulent as theflow rate Q in the second pipe becomes larger, and the pressure gradientΔP becomes too small as the flow rate Q in the second pipe becomessmaller. Accordingly, it may be difficult to control the amount of theliquid added from the second pipe. In the case where the inner diameterD of the second pipe is 0.1 mm or less, the inner diameter of the pipeis too small so that the pressure gradient ΔP becomes too large. As aresult, it may be difficult to control the amount of the liquid addedfrom the second pipe in practice. Therefore, when the inner diameter ofthe second pipe is in the range of more than 0.1 mm and 4 mm or less,the diluted solution can be provided with an accurate componentconcentration as specified.

Advantageous Effects of Invention

According to the present invention, by appropriately controlling thepressure in a tank, which stores a high concentration liquid to bediluted, based on the measured values of the flow rate and the componentconcentration of a diluted solution to be produced, a high concentrationliquid can be precisely added to a diluent medium so as to produce thediluted solution at a specified component concentration. In addition,according to the present invention, a simple apparatus structure isensured.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a concept view showing a diluted solution production apparatusof a first embodiment of the present invention;

FIG. 2 is a concept view showing the diluted solution productionapparatus of a second embodiment of the present invention;

FIG. 3 is a concept view showing the diluted solution productionapparatus of a third embodiment of the present invention;

FIG. 4 is a concept view showing a diluted solution production apparatusof a first example of the present invention;

FIG. 5 is a graph showing fluctuation in water consumption in a point ofuse in the first example;

FIG. 6 is a concept view showing the diluted solution productionapparatus of a second example of the present invention;

FIG. 7 is a concept view showing the diluted solution productionapparatus of a third example of the present invention;

FIG. 8 is a concept view showing the diluted solution productionapparatus of a first comparative example;

FIG. 9 is a concept view showing the diluted solution productionapparatus of a second comparative example:

FIG. 10 is a graph showing the result of examining the relation betweenthe flow rate and the differential pressure between both ends of a pipewhen water is fed to the pipe whose inner diameter varies; and

FIG. 11 is a graph showing the result of examining a relation betweenthe Reynolds number and the differential pressure between both ends ofthe pipe when water is fed to the pipe whose inner diameter varies.

DESCRIPTION OF EMBODIMENTS

Hereinafter, some embodiments of the present invention will be describedwith reference to the drawings.

First Embodiment

FIG. 1 conceptually shows a diluted solution production apparatus of afirst embodiment of the present invention. Although not shown in FIG. 1,components such as filters and valves may be installed in a pipingsystem in the drawing.

The diluted solution production apparatus of the first embodimentincludes first pipe 11 that supplies a first liquid to a point of use,tank 12 that stores a second liquid, and second pipe 13 that suppliesthe second liquid from tank 12 to first pipe 11. The second liquid is achemical liquid to be diluted. The first liquid is a diluent medium,such as pure water that dilutes the second liquid. Therefore, the liquidobtained by supplying the second liquid to the first liquid is a dilutedsolution of the second liquid.

First pipe 11 includes connection 11 a, to which second pipe 13 isconnected, in a middle thereof. On the upstream side of connection 11 ain first pipe 11, flowmeter 14 is installed to measure the flow rate ofthe first liquid flowing through first pipe 11. On the downstream sideof connection 11 a in first pipe 11, meter 15 is installed to measurethe component concentration of the diluted solution.

A method of connecting second pipe 13 to connection 11 a of first pipe11 is not particularly limited as long as the first liquid and thesecond liquid are appropriately mixed. For example, it is preferable toconnect first pipe 11 and second pipe 13 such that the front end ofsecond pipe 13 is positioned in the central portion of first pipe 11because the first liquid and the second liquid are efficiently mixed.

In-tank pressure regulator 16 that adjusts the in-tank pressure to aspecified value is connected to tank 12. The diluted solution productionapparatus of the first embodiment further includes controller 17.Controller 17 calculates the target value of the in-tank pressure thatcauses the component concentration of the diluted solution to be aspecified value based on the measured values of flowmeter 14 and meter15. Controller 17 then controls in-tank pressure regulator 16 so as toadjust the in-tank pressure to the target value.

While in-tank pressure regulator 16 may have any configuration as longas the pressure can immediately be adjusted under a command ofcontroller 17, it is preferable that in-tank pressure regulator 16comprise a gas supplier that supplies inactive gas to an upper side intank 12 and a regulator that adjusts supply pressure of the inactivegas. While the type of the inactive gas is not particularly limited,nitrogen gas is preferable since it can be used relatively easily.Measurement with flowmeter 14 and meter 15 may be performed continuouslyor periodically.

Controller 17 calculates an appropriate level of the amount of thesecond liquid to be supplied with respect to the flow rate of the firstliquid measured with flowmeter 14, in order to adjust the componentconcentration of the diluted solution that is to be produced to aspecified value. Next, controller 17 calculates the target value of thepressure in tank 12 that corresponds to the calculated supply amount. Inthis case, according to the Hagen-Poiseuille law, the relation in whichthe flow rate Q of the second liquid flowing through second pipe 13 isproportional to the pressure gradient ΔP between both ends of the secondpipe 13 is established. Therefore, the pressure in tank 12 may bechanged so that the pressure gradient ΔP changes in proportion to theflow rate of the first liquid with a certain proportionality constant.For example, when the flow rate of the first liquid doubles, thepressure gradient ΔP may also be doubled. When the flow rate of thefirst liquid becomes half, the pressure gradient ΔP may also be halved.By performing such a control method, the proportional relation betweenthe flow rate of the first liquid and the flow rate of the second liquidis maintained accordingly, and the diluted solution that has a stableconcentration can be provided. However, the component concentration,etc. of the second liquid is not necessarily constant due to processessuch as vaporization and degradation of the second liquid in the tank.Therefore, even when, for example, the component concentration of thediluted solution is a specified value at the beginning, the componentconcentration may gradually deviate from the specified value.Accordingly, the diluted solution production apparatus of the firstembodiment has a feedback function including, measuring the componentconcentration of the diluted solution with meter 15; and correcting, ifthe measured component concentration of the diluted solution deviatesfrom the specified value, a proportionality constant so that thecomponent concentration of the diluted solution is adjusted to thespecified value. The feedback function makes it possible to change theproportionality constant to an optimum value without it being necessaryto manually calculate the proportionality constant at the time ofinitial startup of the apparatus or at the time of changing the targetvalue of the component concentration of the diluted solution.

Furthermore, in order to maintain a sufficient proportional relationbetween the flow rate Q and the pressure gradient ΔP, it is preferablethat the second liquid that flows through second pipe 13 be in a laminarflow state as described in [Solution to Problem]. The inner diameter ofsecond pipe 13 is preferably in the range of more than 0.1 mm and 4 mmor less, more preferably in the range of more than 0.1 mm and 1 mm orless.

Second pipe 13 may be made of any material. However, in the case ofproducing a diluted solution for cleaning electronic materials, secondpipe 13 may preferably be made of materials including fluororesin suchas PFA, polyethylene-based resin, and polypropylene-based resin. Amongthese materials, a tube made of fluororesin is particularly preferablesince it elutes less.

While the length of second pipe 13 is not particularly limited, thelength is preferably in the range of 0.01 m or more and 100 m or less,and more preferably in the range of 0.1 m or more and 10 m or less. Itis not preferable that second pipe 13 has a length of 0.01 m or less,because the length is too short to influence the flow rate in the pipe.That is, if second pipe 13 that has a length of 0.01 m or less is used,it becomes difficult to use the pressure gradient ΔP between both endsof the second pipe 13 for proportional control of the flow rate Q of thesecond liquid supplied to first pipe 11. It is not preferable that thesecond pipe 13 has a length of 100 m or more, since not onlyinstallation of the pipe becomes difficult, but also the area of thepipe in contact with the liquid increases, which causes increasedcontamination of the liquid in the pipe.

The number of second pipes 13 to be installed is not particularlylimited. In order to drastically change the dilution ratio, second pipe13 that has an optimal inner diameter and length may be used as needed,depending on an installation condition of the diluted solutionproduction apparatus. The amount of the second liquid that is suppliedis preferably in the range of 10 μL/min or more and 500 mL/min or less.In this range, it becomes possible to accurately control the amount ofthe second liquid that is supplied by using a pipe having an innerdiameter of more than 0.1 mm and 4 mm or less.

The type of the first liquid is not particularly limited. Ultrapurewater, pure water, water containing dissolved electrolyte or gas, andalcohols such as an isopropyl alcohol may be used according to usageapplication. The type of the second liquid is not particularly limitedas long as the second liquid is used in a diluted state. Watercontaining dissolved electrolyte or gas, and alcohols such as anisopropyl alcohol may be used according to usage application.

In the case where a diluted solution produced with the diluted solutionproduction apparatus of the present invention is used for cleaningelectronic materials, ultrapure water may be used as the first liquid,and an aqueous solution containing dissolved electrolyte may be used asthe second liquid. The type of the aqueous solution containing dissolvedelectrolyte is not particularly limited. Examples of the aqueoussolution containing dissolved electrolyte include aqueous solutions ofacid such as hydrochloric acid, sulfuric acid, hydrofluoric acid, nitricacid, and carbonic acid, and aqueous solutions of alkalis such asammonia, potassium hydroxide, and sodium hydroxide. This is because, inrecent years, attention has been paid to the discovery that the cleaningwater, obtained by adding a slight amount of gas constituents orchemicals to ultrapure water, has effects such as removing impurities onthe surface of semiconductor wafers and preventing electrification, thegas constituents including hydrogen, oxygen and ozone, the chemicalsincluding hydrochloric acid, hydrofluoric acid, carbonic acid, andaqueous ammonia.

For example, using dilute aqueous ammonia for cleaning wafers is knownto be effective for preventing electrification during the wafer cleaningprocess, the dilute aqueous ammonia being obtained by diluting highconcentration aqueous ammonia containing 29 wt % ammonia hundreds ofthousands of times with water. In the case where a pump is used fordiluting the high concentration aqueous ammonia (for adding the highconcentration aqueous ammonia to ultrapure water) as disclosed in PatentLiterature 1, it is necessary to preliminarily dilute the highconcentration aqueous ammonia to some extent and then add the dilutedaqueous ammonia with the pump since a high dilution ratio is involved.On the other hand, in the diluted solution production apparatus of thepresent invention, the amount of high concentration aqueous ammonia thatis supplied to ultrapure water can be precisely controlled. This makesit possible skip the preliminary process of diluting the highconcentration aqueous ammonia to some extent.

Flowmeter 14 that measures the flow rate of the diluted solutionproduced in the diluted solution production apparatus of the presentinvention or the first liquid may have any configuration as long asflowmeter 14 has a function of transmitting a measured value tocontroller 17. Examples of flowmeter 14 include a Kalman vortexflowmeter and an ultrasonic flowmeter. Meter 15 may have anyconfiguration as long as meter 15 has functions of measuring thecomponent concentration of the diluted solution as an electrochemicalconstant, and transmitting the measured value. Examples of meter 15include an electric conductivity meter, a pH meter, a resistivity meter,an oxidation-reduction potentiometer (ORP meter), and an ion electrodemeter.

The installation position of flowmeter 14 is not particularly limited aslong as fluctuation in the flow rate inside first pipe 11 that suppliesthe diluted solution to a point of use can be monitored. As shown inFIG. 1, flowmeter 14 may be installed on the upstream side of connection11 a in first pipe 11 to measure the flow rate of the first liquid infirst pipe 11. Alternatively, flowmeter 14 may be installed on thedownstream side of connection 11 a in first pipe 11 to measure the flowrate of the diluted solution that flows through first pipe 11. This isbecause the amount of the second liquid that is supplied is far smallerthan the flow rate of the first liquid, and therefore the flow rate ofthe first liquid can be treated as an equivalent of the flow rate of thediluted solution.

The installation position of meter 15 is on the downstream side ofconnection 11 a in first pipe 11 as shown in FIG. 1. In thisinstallation position, meter 15 may directly be installed in first pipe15, or meter 15 may be installed in a bypass line provided so as tobranch from first pipe 15 and to again be joined to the first pipe 15.

Second Embodiment

FIG. 2 conceptually shows the diluted solution production apparatus of asecond embodiment of the present invention. Here, components similar tothose in the first embodiment are designated by similar reference signs,and differences from the first embodiment will be described mainly.

As shown in FIG. 2, the diluted solution production apparatus of thesecond embodiment includes, in addition to the components of the firstembodiment, pressure gauge 18 that can measure in-pipe pressure atconnection 11 a where second pipe 13 connects to first pipe 11.Furthermore, controller 17 of this embodiment calculates the targetvalue of the pressure in tank 12 that causes the component concentrationof the diluted solution to be a specified value based on the measuredvalues of flowmeter 14, meter 15, and pressure gauge 18. Controller 17then controls in-tank pressure regulator 16 so as to adjust the pressurein tank 12 to the target value.

As is understood from the Hagen-Poiseuille law, the pressure gradient ΔPbetween both ends of the second pipe 13 influences the accuracy of theamount of the second liquid to be supplied. Accordingly, when thepressure at connection 11 a drastically fluctuates, it becomes difficultto stably produce the diluted solution having a specified componentconcentration. In the case of the second embodiment, the pressurefluctuation in connection 11 a can be monitored, so that the amount ofthe second liquid to be supplied can be controlled more accurately, andthe diluted solution with a specified component concentration can bestably provided.

Pressure gauge 18 may have any configuration as long as it has afunction of transmitting the measured value to controller 17. In FIG. 2,the installation position of pressure gauge 18 is on the downstream sideof connection 11 a in first pipe 11. However, the installation positionmay be on the upstream side of connection 11 a in first pipe 11 as longas the in-pipe pressure at connection 11 a can be measured. Therefore,“the in-pipe pressure at connection 11 a” as used herein refers to thein-pipe pressure not only in the just position where second pipe 13connects to first pipe 11 but also in the vicinity of the just position.The phrase “the vicinity of connection 11 a” is used to refer, forexample, to a region within the ranges of 1 m forward and backwardconnection 11 a of first pipe 11.

Third Embodiment

FIG. 3 conceptually shows the diluted solution production apparatus of athird embodiment of the present invention. Here, components similar tothose in the first and second embodiments are designated by similarreference signs, and differences from the first and second embodimentswill be described mainly.

As shown in FIG. 3, the diluted solution production apparatus of thethird embodiment includes, in addition to the components of the firstand second embodiments, connection pressure regulator 19 that adjuststhe in-pipe pressure at connection 11 a to a specified value based onthe measured value of the pressure gauge 18. Furthermore, controller 17of this embodiment calculates the target value of the pressure in tank12 that causes the component concentration of the diluted solution to bea specified value based on the measured values of flowmeter 14, meter15, and pressure gauge IS. Controller 17 then controls in-tank pressureregulator 16 so as to adjust the pressure in tank 12 to the targetvalue. Since the connection pressure regulator 19 adjusts the in-pipepressure at connection 11 a to a specified value, controller 17 maycalculate the target value of the pressure in tank 12 based on themeasured values of flowmeter 14 and meter 15.

As connection pressure regulator 19, any method may be adopted, such asa method of installing a pump on the upstream side of connection 11 a infirst pipe 11 and controlling the number of rotations of the pump so asto adjust the in-pipe pressure at connection 11 a to a specified value.Alternatively, a method of installing an opening adjustment valve may beadopted as connection pressure regulator 19, in which the openingadjustment valve is installed on the upstream or downstream side ofconnection 11 a in first pipe 11 and the opening of the valve iscontrolled so as to adjust the in-pipe pressure at connection 11 a to aspecified value. The method of using the pump is particularly preferablesince the in-pipe pressure at connection 11 a can easily be controlled.The type of the pump to be used is not particularly limited. Examples ofthe pump include a bellows-type pump and a magnetic levitation-typepump.

EXAMPLES

The present invention will now be concretely described based onexamples. The description is illustrative only and is not intended tolimit the present invention. Here, cases of producing, as a dilutedsolution, dilute aqueous ammonia usable for cleaning electronicmaterials will be described as the examples.

First Example

FIG. 4 shows a concept view of a dilute aqueous ammonia productionapparatus of a first example.

First, ultrapure water was fed to first pipe 11 made of PFA Theultrapure water had an electrical resistivity of 18 MΩ·cm or more, and atotal organic carbon (TOC) of 1.0 ppb or less. Next, high concentrationaqueous ammonia containing 29 wt % ammonia (for electronic industry,made by Kanto Chemical Co., Inc.) was supplied as a chemical liquid fromtank 12 made of PFA to the ultrapure water in first pipe 11 throughsecond pipe 13. As a consequence, dilute aqueous ammonia having aspecified component concentration was produced and supplied to a pointof use. As second pipe 13, a pipe made of PFA with an inner diameter of0.3 mm and a length of 1 m was used.

By measuring the electric conductivity of the dilute aqueous ammonia tomonitor the component concentration (ammonia concentration) thereof,dilute aqueous ammonia was produced so as to have an electricconductivity of 20 μS/cm (target value). Specifically, the electricconductivity of the dilute aqueous ammonia was measured with electricconductivity meter 15A. The flow rate of the ultrapure water that flowsthrough first pipe 11 was measured with flowmeter 14. Based on therespective measured values, the target value of the pressure in tank 12was calculated. The target value at that time was a value that couldcause the component concentration of the diluted solution to be aspecified value in accordance with the amount of the high concentrationaqueous ammonia supplied from tank 12 to first pipe 11I. Controller 17then controlled regulator (EVD-1500 made by CKD Corporation) 16A forcontrolling nitrogen gas supplied from a nitrogen gas supply source (notshown) to tank 12, so as to adjust the pressure in tank 12 to coincidewith the target value. As flowmeter 14, an ultrasonic flowmeter(UCUF-20K made by Tokyo Keiso Co., Ltd.) was used. As electricconductivity meter 15A, an electric conductivity meter (M300 made byMettler-Toledo International Inc.) was used.

The control as described above was performed to adjust the electricconductivity of the dilute aqueous ammonia to be produced to 20 μS/cm.This is because the dilute aqueous ammonia for practical use as acleaning liquid for electronic industry is required to have an electricconductivity of 5 to 40 μS/cm.

As shown in FIG. 5, when a produced water amount (water consumption inthe point of use) was changed in a stepwise manner, the electricconductivity of the obtained dilute aqueous ammonia fluctuated between18.3 and 21.9 μS/cm with respect to the target value of 20 μS/cm. Thatis, even when the produced water amount was changed, the supply amountof the high concentration aqueous ammonia immediately followed thechange so as to adjust the electric conductivity of the dilute aqueousammonia being produced to a specified value. As a result, the diluteaqueous ammonia could be produced with stable conductivity. In the test,according to the calculation, the flow rate in second pipe 13 fluctuatedbetween 0.122 and 0.974 mL/min. and the Reynolds number Re at that timewas thought to be 6 to 48. That is, it is thought that the flow in thesecond pipe 13 was a laminar flow.

Second Example

FIG. 6 shows a concept view of a dilute aqueous ammonia productionapparatus of a second example.

In the second example, pressure gauge (HPS made by Surpass Industry Co.,Ltd.) 18A that can measure the pressure of connection 11 a between firstpipe 11 and second pipe 13 was added to the apparatus of the firstexample (FIG. 4). A target value of the pressure in tank 12 wascalculated based on the measured values of flowmeter 14, electricconductivity meter 15A, and pressure gauge 18A. Other configurationalaspects were the same as those of the first example.

When the produced water amount (water consumption in a point of use) waschanged in a stepwise manner as in the first example, the electricconductivity of the obtained dilute aqueous ammonia fluctuated between18.9 and 21.2 μS/cm with respect to a target value of 20 μS/cm. In thesecond example, the dilute aqueous ammonia could be produced with morestable conductivity than that of the first example.

Third Embodiment

FIG. 7 shows a concept view of a dilute aqueous ammonia productionapparatus of a third example.

In the third example, pressure gauge (HPS made by Surpass Industry Co.,Ltd.) 18A that can measure the pressure of connection 11 a between firstpipe 11 and second pipe 13, and magnetic levitation-type supply pump(BPS-4 made by Levitronix Japan K.K.) 19A that uses to adjust thepressure of connection 11 a to a specified value based on the measuredvalue of pressure gauge 18A were added to the apparatus (FIG. 4) of thefirst example. The number of rotations of pump 19A was controlled so asto adjust the measured value of pressure gauge 18A to 280 kPa, and atarget value of the pressure in tank 12 was calculated based on themeasured values of flowmeter 14 and electric conductivity meter 15A.Other configurational aspects were the same as those of the firstexample.

When the water consumption in the point of use was changed in a stepwisemanner as in the first example, the electric conductivity of theobtained dilute aqueous ammonia fluctuated between 193 and 20.5 μS/cmwith respect to the target value of 20 μS/cm. In the third example, thedilute aqueous ammonia could be produced with electric conductivity morestable than that in the second example.

Fourth Example

In a fourth example, dilute aqueous ammonia was produced so as to havean electric conductivity of 5 μS/cm (target value) using a pipe made ofPFA as second pipe 13, the pipe having an inner diameter of 0.2 mm and alength of 3 m. Other configurational aspects were the same as those ofthe third example.

When the produced water amount (water consumption in a point of use) waschanged in a stepwise manner as in the first example, the electricconductivity of the obtained dilute aqueous ammonia fluctuated between4.7 and 5.2 μS/cm with respect to a target value of 5 μS/cm. In thetest, according to the calculation, the flow rate in second pipe 13fluctuated between 0.012 and 0.098 mL/min, and the Reynolds number Re atthat time was thought to be 1 to 7. That is, it is thought that the flowin second pipe 13 was a laminar flow.

First Comparative Example

FIG. 8 shows a concept view of the dilute aqueous ammonia productionapparatus of a first comparative example.

In the first to third examples, a pressure gradient between the tankthat stores high concentration aqueous ammonia and the pipe that carriesultrapure water was taken advantage of to supply high concentrationaqueous ammonia to the ultrapure water. In the first comparativeexample, a pump was used for supplying high concentration aqueousammonia to ultrapure water.

In the first comparative example, high concentration aqueous ammoniacontaining 29 wt % ammonia was stored in primary tank 12A made of PFA,and the high concentration aqueous ammonia was supplied to secondarytank 12B with primary pump 20A and then was diluted 200 times withultrapure water. The diluted aqueous ammonia was supplied to theultrapure water in first pipe 11 with secondary pump 20B. As pumps 20Aand 208, a chemical injection pump (DDA made by Grundfos Pumps K.K.) wasused.

For the amount supplied by secondary pump 20B, a target value of thedischarge pressure of secondary pump 208 was calculated based on themeasured values of flowmeter 14 and electric conductivity meter 15A. Thetarget value at that time was a value that could cause the componentconcentration of the diluted solution to be a specified value inaccordance with the amount of the high concentration aqueous ammoniasupplied from tank 12B to first pipe 11. The configurational aspects,other than the aspect of using the pump to supply the high concentrationaqueous ammonia to the ultrapure water in first pipe 11, were the sameas those of the first example.

When the water consumption in the point of use was changed in a stepwisemanner as in the first example, the electric conductivity of theobtained dilute aqueous ammonia fluctuated between 17.3 and 22.6 μS/cmwith respect to the target value of 20 μS/cm.

Second Comparative Example

FIG. 9 shows a concept view of a dilute aqueous ammonia productionapparatus of a second comparative example.

In the first to third examples, the target value of the in-tank pressurewas calculated based on the measured values of flowmeter 14 and electricconductivity meter 15A. However, in the second comparative example, thetarget value of the in-tank pressure was calculated based only on themeasured value of flowmeter 14. Other configurational aspects were thesame as those of the first example.

When the water consumption in the point of use was changed in a stepwisemanner as in the first example, the electric conductivity of theobtained dilute aqueous ammonia fluctuated between 17.3 and 21.6 μS/cmwith respect to the target value of 20 μS/cm. As compared with the firstexample, the control range of the electric conductivity was widened, andthe electric conductivity, in particular, often became less than thetarget value of 20 μS/cm. This was thought to be because the highconcentration aqueous ammonia in tank 12 vaporized in gaseous phaseduring the production process of the dilute aqueous ammonia, whichcauses the ammonia concentration in tank 12 to become lower than theoriginal specified concentration.

Fifth Example

The following experiment was carried out to determine the range of theinner diameter of the pipe (second pipe 13), which is used for adding aminute amount of a chemical liquid to ultrapure water, in order to allowprecise control of the amount of the chemical liquid to be added. Morespecifically, three types of pipes identical in length and different ininner diameter were prepared to measure a differential pressure (i.e., apressure gradient between both ends of each pipe) when ultrapure waterwas fed to the three pipe. Then, the range in which the flow rate andthe differential pressure had proportional relation was determined. Theprepared three types of pipes were 2 m in length and were ϕ2.5 mm, ϕ4mm, and ϕ6 mm in inner diameter, respectively.

The Reynolds numbers were also calculated based on the flow rate [L/h]when ultrapure water was fed to the pipes and based on the innerdiameters of the pipes [mm]. For calculation, the expression based onthe aforementioned Hagen-Poiseuille law was used: Re=4×Q/(π×D)×ν). Thecoefficient of kinematic viscosity ν was defined as the coefficient ofkinematic viscosity of pure water under atmospheric pressure at 20° C.(1.004×10⁻⁶ (m²/s)).

The result of the above experiment is shown in Table 1 below. FIGS. 10and 11 are graphs showing, based on the data of Table 1, the relationbetween the flow rate and the differential pressure for each of thepipes having different inner diameters and the relation between theReynolds number and the differential pressure for each of the pipeshaving different inner diameters, respectively.

As shown in Table 1, when the flow rate of the water, which passedthrough the pipe having an inner diameter of ϕ2.5 mm, was changed to 5L/h, 10 L/h, 15 L/h, 20 L/h, and 25 L/h, differential pressures in therespective flow rates were 4 kPa, 9 kPa, 14 kPa, 21 kPa, and 28 kPa.When the flow rate exceeded 20 L/h, the inclination of a straight linein the graph of FIG. 10 slightly increased, and the proportionalrelation between the flow rate and the differential pressure no longerheld.

When the flow rate of the water, which passed through the pipe having aninner diameter of 44 am, was changed to 10 L/h, 20 L/h, 30 L/h, 40 L/h,and 50 L/h, differential pressures in the respective flow rates were 1kPa, 3 kPa, 5 kPa, 7 kPa, and 9 kPa. When the flow rate exceeded 30 L/h,the inclination of a straight line of the graph in FIG. 10 slightlyincreased, and the proportional relation between the flow rate and thedifferential pressure no longer held. The calculated Reynolds number Realso exceeded 2300, which indicates that the flow in the pipe was aturbulent flow.

When the flow rate of the water, which passed through the pipe having aninner diameter of ϕ6 mm, was changed to 30 L/h, 50 L/h, 100 L/h, and 150L/h, differential pressures in the respective flow rates were 1 kPa, 3kPa, 8 kPa, and 17 kPa. When the flow rate exceeded 50 L/h, theinclination of a straight line of the graph in FIG. 10 slightlyincreased, and the proportional relation between the flow rate and thedifferential pressure no longer held. The calculated Reynolds number Realso exceeded 2300, which indicates that the flow in the pipe was aturbulent flow.

Table 1 also shows the flow rate, the differential pressure in the flowrate, and the Reynolds number when the water was fed to pipes havinginner diameters of 40.1 mm and 40.2 mm. It should be noted that dataabout the pipes having inner diameters of 40.1 mm and 40.2 mm wereobtained not by experiment but by calculation since the diameters of thepipes were too small. When the flow rate of the water, which passedthrough the pipe having an inner diameter of ϕ0.1 mm, was changed to0.001 L/h, 0.005 L/h, and 0.01 L/h, calculated differential pressures inthe flow rates were 227 kPa, 1127 kPa, and 2268 kPa, respectivelyTherefore, for practical use of such a pipe to add the chemical liquid,a large differential pressure is needed. When comparing this result withdata about the pipe having an inner diameter of 40.2 mm as shown inTable 1, it was found out that the pipe having an inner diameter of 40.1mm needed a considerably larger differential pressure at the same flowrate.

The above results indicate that the inclination of the graphs in FIGS.10 and 11 substantially decreases when the inner diameter of the pipe islarger than ϕ4 mm. That is, when the inner diameter of the pipe islarger than 4 mm, it may be difficult to control the amount of thechemical liquid to be added because a turbulent flow becomes moredominant when the flow rate in the pipe becomes larger and because thedifferential pressure becomes too small when the flow rate in the pipebecomes smaller. On the other hand, when the inner diameter of the pipeis smaller than ϕ2.5 mm, it is thought that the inclination of thegraphs in FIGS. 10 and 11 substantially increases. It may also becomeparticularly difficult to control the amount of the chemical liquid tobe added when, in particular, the differential pressure becomes toolarge due to the inner diameter of the pipe being too small, such as thepipe having an inner diameter of ϕ0.1 mm shown in Table 1.

TABLE 1 Inner diameter Length Flow rate Differential Reynolds of pipe φ[mm] [m] [L/h] pressure [kPa] number 0.1 2 0.001 227   4 0.005 1127  180.01 2268  35 0.2 0.001 14   2 0.005 70   9 0.01 142  18 2.5 5 4  705 109 1418 15 14 2122 20 21 (2827) 25 28 (3531) 4 10 1  886 20 3 1767 30 5(2653) 40 7 (3533) 50 9 (4419) 6 30 1 1768 50 3 (2946) 100 8 (5896) 15017 (8842) * In the table, numerical values in parentheses represent theReynolds numbers included in a turbulent flow range.

REFERENCE SIGNS LIST

-   11 First pipe-   11 a Connection-   12 Tank-   12A Primary tank-   12B Secondary tank-   13 Second pipe-   14 Flowmeter-   15 Meter-   15A Electric conductivity meter-   16 In-tank pressure regulator-   16A Regulator-   17 Controller-   18 18A Pressure gauge-   19 Connection pressure regulator-   19A Metering pump-   20A, 20B Chemical injection pump

What is claimed is:
 1. A diluted solution production apparatus forproducing a diluted solution of a second liquid by adding the secondliquid to a first liquid, the apparatus comprising: a first pipe thatsupplies the first liquid; a tank that stores the second liquid; asecond pipe that supplies the second liquid from the tank to the firstpipe; a flowmeter that measures a flow rate of the first liquid or thediluted solution that flows through the first pipe; a meter thatmeasures a component concentration of the diluted solution, a pressuregauge that measures pressure in the first pipe; a pressure regulatorthat regulates pressure in the tank to adjust a pressure gradientbetween the tank and the first pipe, so as to control an amount of thesecond liquid that is to be added to the first liquid; and a controllerconfigured to calculate a target value of the pressure in the tank thatcauses the component concentration of the diluted solution to bespecified value, based on measured values of the flowmeter, the meter,and the pressure gauge, and that controls the pressure regulator so asto adjust the pressure in the tank to the target value.
 2. The dilutedsolution production apparatus according to claim 1, wherein the secondliquid flows through the second pipe in a laminar flow state.
 3. Thediluted solution production apparatus according to claim 1, wherein thesecond pipe has an inner diameter in a range of more than 0.1 mm and 4mm or less.
 4. The diluted solution production apparatus according toclaim 1, wherein the first pipe supplies ultrapure water as the firstliquid, the second pipe supplies an aqueous solution containingdissolved electrolyte as the second liquid, and the meter measureselectric conductivity as the component concentration of the dilutedsolution.
 5. The diluted solution production apparatus according toclaim 1, wherein the first pipe supplies ultrapure water as the firstliquid, the second pipe supplies an ammonia aqueous solution as thesecond liquid, and the meter measures electric conductivity as thecomponent concentration of the diluted solution.
 6. The diluted solutionproduction apparatus according to claim 1, wherein the pressure gauge isarranged to measure an in-pipe pressure at a connection between thefirst pipe and the second pipe.
 7. The diluted solution productionapparatus according to claim 6, further comprising a connection pressureregulator that adjusts the in-pipe pressure at the connection to aspecified value based on the measured value of the pressure gauge.